Things are moving in the non-musical West End. Jonathan Kent, ex of the Almeida in its most exciting phase, has been appointed artistic director of the Theatre Royal Haymarket for a year-long season. He has opened with a play that, for 170 years, was deemed too filthy to be staged. The Country Wife features a rake who puts it about that he's impotent, in order to do his cuckolding unsuspected; its cast is unflaggingly lascivious, with almost every character out for a joke and a poke. The language is smut-packed: a double entendre about back passages has more loops than Spaghetti Junction.

William Wycherley's 1675 drama, with its exquisite, heartless turns ('I love you almost as much as an intensely new acquaintance,' flutes a wag to his best friend) and its sometimes violent action (a man locks his wife up and threatens her with a blade) has been considered the revenge of Royalists on Puritans and as a glimpse into the black heart of a mercenary society. Jonathan Kent stages it as a romp: fast-moving and fun, but strenuous. Paul Brown's design is bright and glary, and whizzes round between scenes. Toby Stephens is the quintessence of Restoration flounce, with snickering, curled lip and floating limbs. He's one of the few actors to whom the large-scale and florid comes more naturally than televisual restraint, but he's too frothily waggish for the rake Horner (Restoration playwrights didn't hold back on names), this demonic penis, whose flippancy lights up the void at the centre of the world Wycherley writes about.

Patricia Hodge invariably causes a ripple with her creamy hauteur every time she appears, though she heaves her alabaster breasts aloft as if they had just alighted on her body. David Haig comes closest to Wycherley's hysterical blackness. As the cuckolded Pinchwife, he scurries back and forth in a cloud of anxiety, consulting the audience at points of high improbability ('What do you think?'). At one point, his giggling agitation seems to lift him skywards.

Shadowlands, about the late-flowering love between CS Lewis and Joy Davidman, the American fan who became his wife, is another West End surprise. The plot of William Nicholson's 1990 play sounds like Love Story in tweeds. An unlikely couple meet in an Oxford college (where dons in paper hats crack Latin jokes): he's pullovered and repressed and pure English Establishment; she's American and, therefore, frank, with an abrasive tongue and an outsider's eye. She gets cancer; he falls in love; she dies; his life is changed and his faith altered.

Michael Barker-Caven's production slushes up the story where it can: Matthew Wright's dreary design of towering bookcases glides away as the sound of heavenly choirs rings out, to reveal a Narnia-style walk-in wardrobe glowing with ruby light.

Yet the play survives. Despite the fustiness of its setting and set-up, Nicholson's dialogue is often robust and pointed and his concerns, about the impact of suffering on faith and, particularly, the overwhelming impact of bereavement on a child, very well dramatised. John Standing is creepily persuasive as one of the crabbiest of the misogynist dons. But it is the two central performances that give Shadowlands wings. Janie Deet is on the button as Joy: perky, invasive, annoying and true. Charles Dance, lean, slippered and short on whiskery bluffness, at first looks like strange casting for Lewis. The opposite proves the case. Halting, shifting from foot to foot, he looks like someone who's shuffling his skin on like a suit. He suggests he is damp and unvisited. Unlike this production.